(a) Technical Field
The present invention relates to a steering apparatus for a HEV which assists in providing steering power for a driver independent of engine operation, and a method of controlling the same.
(b) Background Art
In general, a hybrid electric vehicle (HEV) refers to a vehicle in which a non-internal combustion engine is combined with an electric motor to improve the fuel efficiency of the internal combustion engine. A hybrid electric vehicle is capable of traveling in a pure electric vehicle (EV) mode, a pure internal combustion mode and a hybrid electric (HEV) mode. In a pure electric mode, power from a motor is transmitted to a transmission so that only the power from the motor is used to power the vehicle. Additionally, hybrid electric vehicles also often include a battery charging mode in which an engine or regenerative braking is used to recharge the battery which is used to provide power to the motor.
In a hybrid vehicle, since a clutch is arranged between the engine and the motor to transmit a power from the engine to a driving shaft, in an HEV travel mode power from the motor can be used to act as an auxiliary power source while the engine acts as a main power source.
Most hybrid electric buses employ a hydraulic pump directly connected to an engine to assist in providing steering power to a driver like a conventional bus. However, an engine is frequently stopped, for example, in the EV travel mode to improve fuel ratio due to characteristics of the hybrid electric vehicle, in which case since the hydraulic pump which assists in providing power for steering is also stopped, power steering is not available while the engine is not running and thus it is difficult for the driver to steer.
Further, the hybrid electric vehicle utilizes engine which output a lower amount of power which can be applied to the hydraulic pump model (for example, 290 ps→240 ps), in which case the typical hydraulic pump cannot be used, thus a hydraulic pump which can operate on less pressure should be used in a hybrid vehicle. However, such a hydraulic pump would not be sufficient to operate a steering apparatus for a vehicle such as a large truck or bus.